This research is designed to yield information that will lead to more effective chemotherapy of human leprosy. In addition, studies designed to answer questions of pathogenesis and to produce information leading to effective immunotherapy will be carried out. Drugs will be screened in the mouse foot pad infection by M. leprae for activity against the organism, with particular emphasis on mycobacterial dihydrofolate reductase inhibitors, 10-phenylphenazines, substituted salicylates, analogs and derivatives of hydnocarpic acid, methimazole, and 2-amino-5-(1-methyl-5-nitro-2-imidazolyl)-1, 3,4-thiadiazole, and any new antimicrobal agents introduced for use in tuberculosis. Pharmacologic studies on effective agents will be carried out. A variety of immunologic studies will be carried out, including studies of interferon and interferon inducers, of protection by a variety of related and unrelated organisms, and of the reactivity of mouse lymphocytes both in vivo and in vitro.